Relating to injection devices

ABSTRACT

An injection device for a syringe incorporates housing for a syringe. A needle shroud is captive to the leading end of the housing and is movable before use between extended and retracted positions. A drive member is releasable from a rearward position within the housing to urge the syringe forwards to project its needle beyond the retracted needle shroud and then to express a dose through the needle. Locating members on the housing capture the drive member at its forward position (attained after expressing the dose). The captured drive member is also arranged to block retraction of the needle shroud from its extended position.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending application Ser. No.10/485,087 filed on Jun. 7, 2004, which is the 35 U.S.C. §371 nationalstage of International PCT/GB02/03428 filed on Jul. 26, 2002, whichclaims priority to British Application No. 0118419.1 filed on Jul. 28,2001. The entire contents of each of the above-identified applicationsare hereby incorporated by reference. Any disclaimer that may haveoccurred during prosecution of the above referenced applications ishereby expressly disclaimed.

BACKGROUND OF THE INVENTION

This invention relates to injection devices. It is concerned with thosewhere a syringe is enclosed in a housing of barrel-like form, thesyringe being propelled forward by a drive mechanism to project itsneedle, followed by continued operation of the drive mechanism to pushthe plunger of the syringe and eject a dose. This will leave the needlesticking out, unless certain measures are taken. One answer is to havean arrangement for withdrawing the syringe back into the housing, whileanother is to have a needle shroud that moves out from the housing toenclose the needle. Of course, this must not interfere with the actualinjection operation. It has therefore been proposed that the shroud isnormally spring-urged forwardly to a needle protecting position, butwhen the device is pushed against the patient's skin the shroud isforced to retract against its spring. After injection, the spring pushesthe shroud forwards again.

It is desirable for there to be an arrangement for automatically lockingthe shroud at its fully projecting position after the injection but notbefore, and it is the aim of this invention to provide a way ofachieving this.

SUMMARY OF THE INVENTION

According to the present invention there is provided an injection devicefor a syringe, the device comprising a housing for the syringe, a needleshroud captive to the leading end of the housing and movable before usebetween extended and retracted positions, a drive member releasable froma rearward position within the housing to urge the syringe forwards toproject its needle beyond the retracted needle shroud and then toexpress a dose through the needle, and locating members on the housingfor capturing the drive member at its forward position attained afterexpressing the dose, and wherein the captured drive member is arrangedto block retraction of the needle shroud from its extended position.

The needle shroud will normally be biased forwardly so that, in use, asthe device is pressed against the skin, the shroud is pushed back intothe housing. The user will then release the drive member.

That drive member will generally be spring-actuated, and in thepreferred form it will have a plunger that enters the rear end of thesyringe to engage the piston within the syringe, thereby supporting thesyringe at its rear end. The needle of the syringe will ideally have acollapsible rubber sheath, which acts as a support for the forward endof the syringe. The tip of the sheath may be located in a small cup-likeformation of the housing with a central aperture through which theneedle, but not the sheath, can penetrate. As the syringe is drivenforwards, the needle pierces the sheath to project through and beyondthe cup-like formation while the sheath “concertinas” into a shorterlength, helping to arrest the syringe when it is fully compressed.

The drive member may have arms that extend forwardly to co-operate withthe interior of the housing and the needle shroud. As the drive membermoves forwards, these arms can be flexed inwards by locating formationson the housing to cause their leading ends to enter the retracted needleshroud. After the injection, as the needle shroud is released and movesforwards, it passes beyond the arms, which disengage and flex backoutwards. Abutments on the outsides of the arms can then be provided tobe in registry with abutments on the inside of the housing, aftercompletion of the injection operation, so that the drive member cannotbe pushed back. Preferably these abutments will be hooked for positiveinterengagement. At the same time, after completion of the injectionoperation, the ends of the arms are ideally aligned with the needleshroud, and provide abutments to prevent the shroud being pushed back.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, one embodiment will now bedescribed, by way of example, with reference to the accompanyingdrawings, in which:

FIGS. 1 to 6 are axial sections of an injection device in various stagesfrom pre-use to post-use,

FIG. 7 is an enlarged detail of FIG. 6, and

FIGS. 8 and 9 are perspective views of a drive member of the device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The injection device has a composite barrel 1 with a rear portion 2having a closed rear end 3, an intermediate portion 4, and a forwardportion 5. The intermediate portion 4 carries a co-axial inner tube 6 byradial spokes 7 immediately to the rear of a forward facing innershoulder 8. The leading end 9 of the tube 6 constricts and has a smallaperture 10 formed by an inward annular flange 11 at its extremity. Twodiametrically opposed lugs project inwardly and forwardly from theshoulder 8, which locates the rear end of a helical spring 13.Cradle-like or U-shaped guides 14 as best seen in FIG. 7 are formed onthe outside of the tube 6 directly opposite these lugs 12. At itsforward end the spring 13 bears against a needle shroud 15 made captiveto the barrel by the forward portion 5 but capable of sliding backwards,telescoping further into the barrel to compress the spring 13 and tonest closely over the leading end 9 of the tube 6.

The rear end 3 internally provides a seat for a drive spring 16 whichacts on a drive member 17 as best seen in FIGS. 8 and 9. It has a hollowcylindrical portion 18 to receive the forward end of the spring 16,which also locates around an x-section stem 19 co-axially within theportion 18 and projecting rearwardly beyond it. Forward of this, thecylinder 18 steps inwards to a co-axial intermediate portion 20 solidapart from a transverse bore 21, and then steps further inwards into aco-axial plunger with a central bore 23 open to its leading end.Branching out and then forwardly from the intermediate portion 20 thereare two diametrically opposed arms 24 with outwardly projecting lugs 25at their free ends, and each with a tooth 26 a short distance back fromthe lug 25. Each tooth 26 slopes at an acute angle outwardly andrearwardly and then slants back in at a less acute angle. On one sidethe cylinder 18 has a forwardly and outwardly projecting tongue 27 whichis part of the trigger mechanism for releasing the drive member 17, andopposite that tongue there is a longitudinal heel 28 which can run in atrack (not shown) formed on the inside of the barrel 1 to ensure thatthe drive member 17 is correctly orientated and runs true.

A conventional syringe 29 is co-axially carried within the tube 6. Itsneedle 30 has a rubber sheath 31 whose closed forward end locates in thecup-like leading end 9 of the tube 6. The sheath 31 is never removed,but it is shown only in FIGS. 1 and 4. The plunger 22 of the drivemember 17 enters the rear end of the syringe and co-operates with itspiston 32, which has a rear central stud 33 that locates in the bore 23.The syringe 29 is thus carried co-axially within the tube 6 by the tipof the sheath 31 and the stud 33: there is no contact between the bodyof the syringe and the tube 6.

Initially, the device is made safe by a pin (not shown) transverselythrough the barrel 1 and through the bore 21, locking the drive member17 in its rearward position with the spring 16 compressed, as in FIG. 1.When this pin is removed, the device can be fired. The user firstpresses the leading end of the needle shroud 15 against the area to beinjected and urges the device forwards. The needle shroud 15 is forcedback until the spring 13 is fully compressed. The sheathed tip of theneedle 30 is still within the device, which has now reached the positionof FIG. 3.

The trigger is operated, allowing the spring 16 to act, and that drivesthe member 17 forwards. The effective solidity of the dose within thesyringe 29 causes that to be moved forwards to project the needle 30,which pierces the end of the sheath 31, leaving that to concertina intoa short length within the leading end 9 as indicated in FIG. 4. It istoo bulky to pass through the aperture 10. The needle 30 thereforeenters the flesh. During this movement, the lugs 25 and 12 meet. Thelatter may be deflected slightly outwardly but any such movement will belimited by the compressed spring 13. The arms 24, however, will beflexed inwardly, allowing the lugs 25 to snap past and bear outwardlyagainst the inside of the shroud 15. The arms 24 start to pass throughthe guides 14 at this time and they help to keep the arms properlyaligned. The syringe 29 reaches the limit of its forward movement by thesheath 31 becoming fully compressed, the teeth 26 simultaneously comingup against the rear sloping sides of the lugs 12. This is the positionof FIG. 4.

Continued forward movement of the member 17 ejects the dose through theneedle 30 and causes the teeth 26 and lugs 12 to act as wedges and flexthe arms 24 further inwards. The teeth 26 go past the lugs 12 justbefore the injection is finished, which is when the intermediate portion20 of the drive member 17 comes up against the rear end of the syringe,as shown in FIG. 5. The device is then withdrawn, and this allows thespring 13 to act and push the needle shroud 15 forward again, slidingfree of the teeth 26 and then the lugs 25. The arms 24 can then springoutwards again to their natural positions, and this causes the teeth 26to hook with the lugs 12 if there is any reverse movement. If the needleshroud 15 is pushed back against the lugs 25 and then twisted, pushingthe ends of the arms 24 circumferentially, the guides 14 will resistthis and keep the teeth 26 in registry with the lugs 12.

Thus, the drive member 17 is held against retraction, while the needleshroud 15, still trapped by the forward barrel portion 5 againstremoval, is prevented from rearward movement by abutment with the lugs25. The needle 30, therefore, although still projecting from the tube 6,is safely inside the shroud 15.

What is claimed is:
 1. An injection device for a syringe having aneedle, the device comprising: a housing for receiving in use a syringefor movement with respect thereto; a needle shroud captive to a leadingend of the housing and movable before use between extended and retractedpositions; a drive member configured to move from a rearward positionwithin the housing to urge the syringe and thereby move the syringeforward in the housing to project the needle beyond the needle shroudwhen the needle shroud is in the retracted position, and then to aforward position to express a dose through the needle; and locatingmembers on a sidewall of the housing, said locating members configuredto, upon arrival of the drive member into the forward position, captureand maintain the drive member at the forward position attained afterexpressing the dose, the captured drive member being prevented by saidlocating members from rearwardly exiting the forward position, wherein,when the drive member is captured by the locating members, a blockingportion of the drive member is positioned to stop a rearward retractionof the needle shroud from the extended position and, with the drivemember captured by the locating members and stopping the needle shroudfrom retracting from the extended position, an entire length of theneedle is shrouded by said needle shroud.
 2. The injection deviceaccording to claim 1, wherein the drive member has arms that extendforwardly to co-operate with an interior of the housing and the needleshroud.
 3. The injection device according to claim 2, wherein locatingformations on the housing are provided to cause leading ends of the armsto be flexed inwards and to enter the retracted needle shroud.
 4. Theinjection device according to claim 3, wherein the arms include outwardfacing abutments that are in registry with said locating formations onthe inside of the housing, so that when the dose has been expressed, thedrive member is prevented from being pushed back from the forwardposition.
 5. The injection device according to claim 4, wherein saidabutments are hooked for positive interengagement.
 6. The injectiondevice according to claim 2, wherein the ends of the arms are alignedwith the needle shroud when the injection operation is complete, andprovide abutments to prevent the needle shroud from being pushed backfrom the extended position to the retracted position.
 7. The injectiondevice according to claim 1, wherein the drive member isspring-actuated.
 8. The injection device according to claim 7, whereinthe drive member has a plunger that enters a rear end of the syringe toengage a piston within the syringe, thereby supporting the syringe atthe rear end.
 9. The injection device according to claim 1, wherein theneedle of the syringe has a collapsible rubber sheath which acts as asupport for a forward end of the syringe.
 10. The injection deviceaccording to claim 9, wherein a tip of the sheath is located in a smallcup-like formation of the housing provided with a central aperturethrough which the needle, but not the sheath, can penetrate.
 11. Theinjection device according to claim 1, wherein the needle shroud isbiased forwardly so that, in use, when the device is pressed against theskin, the shroud is pushed back into the housing.
 12. The injectiondevice according to claim 1, wherein the drive member is provided withrespective abutment surfaces that snap past the locating members on theside wall of the housing as the drive member moves towards said forwardposition, the locating members configured to cooperate with the abutmentsurfaces to capture said drive member and prevent said drive member fromreturning from the forward position.
 13. The injection device accordingto claim 1, wherein the locating members and the drive member areconfigured to enter into locking engagement with each other upon arrivalof the drive member into the forward position, the locking engagementpreventing the drive member from exiting the forward position by arearward movement.
 14. The injection device according to claim 1,wherein the drive member comprises elements configured to pass over thelocating members during a forward movement of the drive member from therearward position to the forward position and, upon passing the locatingmembers, engage in locking engagement with the locating members to stopa rearward movement of the drive member from the forward position. 15.An injection device for a syringe having a needle, the devicecomprising: a housing for receiving in use a syringe movable withrespect thereto; a needle shroud captive to a leading end of the housingand movable before use between extended and retracted positions; a drivemember, movable within the housing from a rearward position to aterminal forward position to push the syringe forward in the housingsuch that the needle of the syringe projects outside the needle shroudwhen the needle shroud is in the retracted position and then to causethe syringe to express a dose through the needle before reaching theforward position; and locating members, on a sidewall of the housing,configured to engage in a locking engagement with portions of the drivemember such that the locking members capture the drive member and stopthe drive member from exiting the forward position attained by the drivemember after expressing the dose, wherein, when the drive member is inlocking engagement with the locating members, an abutment portion of thecaptured drive member obstructs a rearward motion of the needle shroudfrom the extended position thereby preventing the needle shroud fromrearwardly exiting the extended position and, with the drive membercaptured by the locating members and obstructing the needle shroud fromretracting from the extended position, an entire length of the needle isshrouded by said needle shroud.
 16. The injection device according toclaim 15, wherein the drive member has a plunger that enters a rear endof the syringe to engage a piston within the syringe, thereby supportingthe syringe at the rear end.
 17. The injection device according to claim15, wherein the abutment portion of the drive member comprises an armconfigured to co-operate with locating formations on an interior of thehousing, the locating formations configured to cause an end of the armto flex into a position for engagement with the needle shroud.
 18. Theinjection device according to claim 15, wherein the abutment portion ofthe drive member comprises a flexible arm that, when the drive member iscaptured in the forward position, is in alignment with a portion of theneedle shroud such that, upon application of a rearward force to theneedle shroud, the abutment portion engages with the needle shroud andprevents the needle shroud from exiting the extended position.
 19. Theinjection device according to claim 15, wherein the drive membercomprises elements configured to pass over the locating members during aforward movement of the drive member from the rearward position to theforward position and, upon passing the locating members, engage inlocking engagement with the locating members to stop a rearward movementof the drive member from the forward position.